Light source device for use in a copying machine

ABSTRACT

A light source device for use in a color copying machine comprises a plurality of light source lamps having different efficiencies respectively and means for lighting any number of light source lamp or lamps among said plural light source lamps depending on the luminous energy of the respective blue, green and red spectrums and/or the spectral sensitivity of the photosensitive member for said respective spectrums.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to a light source device for use in acolor copying machine in which a light bundle is generated by the lightsource device toward an original document and in which acolor-separation of the reflection light reflected by the originaldocument is performed, thereby applying the color-separated light to aphoto-sensitive member so as to form a color image.

DESCRIPTION OF THE PRIOR ART

In recent years, in various kinds of copying machines adopting anelectro-photographic method, there is a kind of copying machine capableof forming a full color image. A full color image is formed in a manneras follows.

First, a reflection light reflected by an original document is appliedto an optical color-separation filter through which a spectrum of a bluewavelength band is passed and projected onto a photo-sensitive member soas to form an electrostatic latent image. Subsequently, yellow toner ismade adhere onto the electrostatic latent image and then the yellowtoner adhering image is transferred to a transfer charger. Similarly,the reflection light reflected by the original document is applied to anoptical color-separation filter through which a spectrum of a greenwavelength is passed and projected onto the photosensitive member so asto form an electrostatic latent image, so that a magenta toner adheringimage is formed to be transferred onto the yellow toner adhering image.Moreover, the reflection light reflected by the original document isapplied to an optical color-separation filter through which a spectrumof a red wavelength is passed, so that a cyanic toner adhering image isformed to be transferred onto the yellow and magenta toner images. Bythese processes mentioned above, there is formed a compound image withyellow, magenta and cyanic toners, i.e., a full color image is formed onthe transfer charger.

When a full color image is formed, the densities of the chromaticitiesof the three kinds of toner images with yellow, magenta and cyanictoners should be made regular and constant in order to preventoccurrence of a specific irregular coloration in the image to be formed.In other words, when an original document with the same density of thechromaticities of blue, green and red is copied, the density of thechromaticities of the three primary colors of the image to be formedshould be made regular as those of the original document. However, inpractical use, the above mentioned densities of the chromaticities ofthe three primary colors of the image to be formed are not made regularowing mainly to a spectral distribution of a light intensity generatedby a light source and to a spectral sensitivity of the photosensitivemember.

FIG. 1 shows a distribution of spectral intensities of a light emittedby a halogen tungsten lamp which is generally used as a light sourcelamp in a copying machine. As shown in FIG. 1, the distribution of thespectral intensities (relative energy ratio) of the light emitted by thehalogen tungsten lamp of the light source becomes lower to higher as thewavelength band of the spectrum goes from the blue short spectrum to thered long spectrum.

FIG. 2 shows a distribution of spectral sensitivities of thephoto-sensitive member provided in the copying machine, wherein thespectral sensitivities become highest at the green wavelength band andbecome lower in the ranges of the blue and red wavelength bands.Therefore, when an original document is copied to form an image thereofby a copying machine using the light source lamp and photo-sensitivemember as mentioned above, the density of the chromaticity of the yellowtoner image becomes rather higher compared to those of the magenta andcyanic toner images, and therefore, there has been a problem that thewhole part of the image to be formed becomes rather yellow colored.

Therefore, there have been made various kinds of devices in order toincrease the quantity of the spectral intensity of the blue wavelengthband of the light emitted by the light source lamp in the prior art. Forexample, (1) there is employed a color-separation filter with highpermeability for a spectrum of a blue wavelength band, (2) there isemployed a color-separation filter permeable for a spectrum of awavelength band shifted to rather a longer wavelength, (3) there areprovided a plurality of light source lamps, (4) there is used a lightsource lamp with high efficiency (herein "lamp efficiency" means a ratiobetween a light energy and a consumed electric power of a lamp (lm/W)),and (5) power supply for a light source lamp is increased, whereby thequantity of the spectral intensity of a blue wavelength band of thelight is increased.

However, the methods (1) to (5) mentioned above have faults respectivelyas follows.

(1) There is a limit (90% degree) for increasing the permeability of thelight permeable filter, and therefore, it is impossible to perform asufficient color correction.

(2) The reproductivity of the yellow and green colors of a documentbecomes worse because of the shift of the permeable wavelength band ofthe filter.

(3) The temperature inside the copying machine rises.

(4) The life of the light source lamp with high efficiency is reduced.

(5) Since the consumption power available in the entire parts of thecopying machine is predetermined, a large increment of the consumptionpower can not be attained.

SUMMARY OF THE INVENTION

The present invention has been made considering the problem mentionedabove, and an essential object of the present invention is to provide alight source device for use in a copying machine, wherein even in thecase a spectrum of a wavelength band of a low value in a spectraldistribution is projected, or a spectrum of a wavelength band for whichthe photosensitive member has a poor photosensitivity is projected, alarge quantity of the spectrum can be obtained.

The present invention is characterized in that, in a copying machine forforming a color image of an original document by performing acolor-separation of a reflection light which is projected from a lampfor light source and reflected by the original document so as to beapplied onto a photosensitive member,

there are provided a plurality of lamps for light source each having adifferent lamp efficiency of electric-photo conversion, and there isprovided means for turning on any one or more lamps for light source ofsaid plurality of light source lamps depending on the quantity of thespectrums in the light generated by the light source lamps and/or, onthe spectral sensitivity of said photosensitive member.

In a light source device for use in a copying machine according to thepresent invention, the quantity of the light generated by the lightsource lamps can be appropriately controlled by changing the efficiencyand the number of the light source lamps to be turned on depending onthe quantity of the spectrums and/or on the spectral sensitivity of thephotosensitive member. For example, in the case there is formed an imagewith a color toner by projecting a spectrum of a wavelength bandcorresponding to a low value in a spectral distribution of the lightgenerated by the light source lamp, or in the case there is formed animage with a color toner corresponding to a spectral wavelength band forwhich the spectral sensitivity of the photsensitive member is low, thereare used one or more light source lamps with good efficiency or thenumber of the light source lamps to be turned on is increased, and onthe contrary, in the case there is formed an image with a color tonercorresponding to a wavelength band of a high spectral distribution ofthe light generated by the light source lamps, or in the case there isformed an image with a color toner corresponding to a wavelength bandfor which the spectral sensitivity of the photosensitive member is high,there are used light source lamps with low efficiency or the number ofthe light source lamps to be turned on is reduced. Hereby, the quantityof the spectrum corresponding to a wavelength band of a low spectraldistribution of the light generated by the light source lamps can beincreased and the quantity of the spectrum corresponding to a wavelengthband for which the spectral sensitivity of the photosensitive member islow can be increased, so that the lack of the quantity of light to beapplied to an original document and the low spectral sensitivity of thephotosensitive member can be compensated. Therefore, when a copyingoperation is performed on an original document with regular density ofthe chromaticity of the respective three primary colors, there appearsno irregularity in the chromatic density of the image to be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a spectral distribution of a quantity of lightgenerated by a halogen tungsten lamp,

FIG. 2 is a graph showing a spectral sensitivity of a photosensitivemember,

FIG. 3 is a schematic front view showing an embodiment of a full colorcopying machine according to the present invention,

FIG. 4 is a graph showing a relation between a lamp efficiency and alife time of a light source lamp used in the copying machine shown inFIG. 3,

FIG. 5 is a graph showing a transmittance of a color-separation filter,

FIG. 6 is a block diagram showing a controller used in the copyingmachine shown in FIG. 3, and

FIG. 7 is a flow chart showing a procedure of an optical system in afull color copying operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, in a generally central portion of a copying machine body, aphotosensitive member 1 of a belt shape is laid between two rollers inright and left sides in a rolling manner around said two rollers. In theperipherals of the photosensitive belt 1, there are provided imageforming devices such as a charger 11, developing vessels 12a to 12c anda transfer device 13. The developing vessels 12a, 12b and 12c containyellow, magenta and cyanic toner respectively. The transfer device 13comprises a belt shaped induction sheet member and a first transfercharger 13a which is installed in a position facing to the abutmentposition with the left roller in the photosensitive member 1. Moreover,a second transfer charger 13b is installed in a position for carrying acopying sheet (to be described later) below the transfer device 13.

A platen 2 for placing an original document is provided on the topportion of the copying machine body and below the platen 2 is providedan optical system comprising light source lamps 21 and 22, totalreflection mirrors 23 to 27, a lens assembly 28 and a color-separationfilter 29. The light source lamps 21 and 22 have respectively their lampefficiencies of 21.6 lm/W and 25 lm/W. The light source lamp 21 isturned on all the time of three processes of blue, green and red colorcopying operations to be described later when a full color copyingoperation is performed but the light source lamp 22 is turned on only inthe process of a copying operation with blue spectrum. In other words,the light source lamp 21 is lighted for a period three times longer thanthe light source lamp 22.

FIG. 4 shows a relation between the lamp efficiency and the life of thelight source lamp. As shown in FIG. 4, the life of the light source lamp21 having a lamp efficiency of 21.6 lm/W is about 150 hours and the lifeof the light source lamp 22 having a lamp efficiency of 25 lm/W is about50 hours. That is to say, the life of the light source lamp 21 having alamp efficiency of 21.6 lm/W is generally three times longer than thatof the light source lamp 22 having a lamp efficiency of 25 lm/W.Accordingly, in practical use of the light source lamps 21 and 22 in thecopying operation, the life of the light source lamp 21 becomesgenerally equal to that of the light source lamp 22.

Next, in case of considering the luminous energy (quantity of lightbundle), when an electric power of 300 watts with 85 volts is suppliedto the light source lamp 21 having an efficiency of 21.6 lm/W, the totalluminous energy of the light bundle becomes 21.6×300=6480 (lm).Moreover, when an electric power of 300 watts with 85 volts is suppliedto the light source lamp 22 having an efficiency of 25 lm/W, the totalluminous energy of the light bundle becomes 25×300=7500 (lm).

If a light source lamp of 21.6 lm/W and a light source lamp of 25 lm/Ware used together when a yellow image is formed with yellow toner, theluminous energy of the total light bundles of the two light sources canbe sufficiently increased compared to the luminous energy when two lightsource lamps having the same efficiency of 21.6 lm/W are used under thesame condition as mentioned above. Even though two light source lamps of21.6 lm/W are also used when the yellow image is formed, the luminousenergy of the two lamps is not rather sufficient to absorb thedifference of the densities of the image, therefore, it is impossible toform an image with sufficient density.

That is to say, comparing the case of using two light source lamps of21.6 lm/W with the case of using a light source lamp of 21.6 lm/W and alight source lamp of 25 lm/W, the relation between the respective ratioof total luminous energy and the ratio of voltages is represented asfollows,

    F/F0=(V/V0)3.19

herein,

F : total luminous energy at the time of input V

F0: total luminous energy at the time of input V0.

And in order to obtain the same luminous energy with a light source lampof 25 lm/W instead of a light source lamp of 21.6 lm/W, the necessaryvoltage is as follows.

    6480/7500=(x/85)3.19

    x=81.2(V)

Accordingly, if a light source lamp of 25 lm/W and a light source lampof 21.6 lm/W are used together, the luminous energy can be increased bya voltage of 3.8 volts compared to the case of using two light sourcelamps of 21.6 lm/W. As described above, since a light source lamp withhigh lamp efficiency is used for lighting for a short time, the luminousenergy can be more increased. Moreover, since the lamp efficiency isgood, even though the life of the lamp becomes short, there occurs noproblem because of few times of lighting on.

The color-separation filter device 29 comprises three filters, i.e., ablue filter 29a which is permeable for a spectrum of a blue wavelengthband, a green filter 29b which is permeable for a spectrum of a greenwavelength band and a red filter 29c which is permeable for a spectrumof a red wavelength band respectively and the three filters mentionedabove are removably provided in the optical path of the reflection lightreflected by the original document. FIG. 5 shows the transmittance ofthe respective filters 29a, 29b and 29c. In addition, in the lowerportion of the copying machine body, there is provided a sheet carriageportion 3 including sheet feeding cassettes 31 and 32 and a fixingdevice 33, in which a copying sheet is carried through the transferdevice 13.

FIG. 6 is a block diagram of a controller unit of the copying machine.

The control of the entire parts of the copying machine is performed by acentral processing unit (referred to as CPU hereinafter) 41. There isprovided an operation panel (not shown) on the top surface of thecopying machine body, in which various signals such as a full colorcopying starting signal are entered through an operation panelcontroller 42. In response to these input signals, the CPU 41 transmitsoperational signals from an input/output unit I/O of the CPU 41 to alight source lamp control unit 43 and a color separation filter controlunit 44 in the optical system of the copying machine. The light sourcelamp control unit 43 controls the on/off operation of the light sourcelamps 21 and 22 and the color separation filter control unit 44 operatesdriving units 44a to 44c of the respective color separation filters 29ato 29c permeable for blue, green and red spectrums respectively so as toinstall one of the three kinds of color separation filters 29a to 29c inthe optical path of the reflection light reflected by the originaldocument.

Next, in FIG. 7, when the full color copying operation is started, it isjudged in step n1 which kind (or color) of the color-separation filter29 is installed in the optical path of the reflection light reflected bythe original document. In case the blue color-separation filter 29a isinstalled in the optical path, both of the light source lamps 21 and 22are turned on in step n2 and the original document is scanned by thelight generated by the light source lamps 21 and 22 in step n3 and thereflection light reflected by the original document is applied to thephotosensitive member 1 through the blue color-separation filter 29a. Inthe case the light source lamps 21 and 22 are both turned on, the totalluminous energy of the light bundles generated by the two light sourcelamps 21 and 22 is 6480+7500=13980 (lm), and therefore, even though thequantity of the spectrum of the blue wavelength band is little includedin the light generated by the halogen tungsten lamp (see FIG. 1), oreven though the photosensitivity of the photsensitive member 1 for theblue wavelength band is low (see FIG. 2), the photosensitive member 1can be exposed with sufficient quantity of the spectrum. Anelectrostatic latent image is formed on the photosensitive member 1 byprojecting the blue spectrum transmitted through the bluecolor-separation filter 29a onto the photosensitive member 1 and thereis fed yellow toner from the developing vessel 12a so as to be madeadhere onto the electrostatic latent image. The yellow image formed withyellow toner is transferred onto the transfer member 13 through thefirst transfer charger 13a.

When the first scanning operation of the original document is completed,the blue color-separation filter 29a is removed in step n4, andsubsequently, the green color-separation filter 29b is installed andthen the red color-separation filter 29c are installed in turn in theoptical path of the reflection light reflected by the original document.When the green color-separation filter 29b is installed in the opticalpath of the reflection light reflected by the original document, onlythe light source lamp 21 is turned on and the original document isscanned by the light generated by the light source lamp 21 in steps n5and n6. Accordingly, the quantity of the light bundle at the time ofusing the green color-separation filter 29b is less than a half of thequantity of the total light bundles at the time of using the bluecolor-separation filter 29a, but under consideration of the spectraldistribution of the light source lamp shown in FIG. 1 and the spectralsensitivity of the photosensitive member 1 shown in FIG. 2 together withthe transmittance of the filter shown in FIG. 5, the quantity of thecharge on the photosensitive member 1 cancelled by the transmissionspectrum transmitted through the blue color-separation filter 29abecomes generally equal to the quantity of the charge on thephotosensitive member 1 cancelled by the transmission spectrumtransmitted through the green color-separation filter 29b in the casethe densities of the chromaticities of the original document areregular. Onto the electrostatic latent image formed on thephotosensitive member 1 by projecting the spectrum transmitted throughthe green color-separation filter 29b, there is fed magenta toner fromthe developing vessel 12b so as to be fixed onto the electrostaticlatent image. And the image with the magenta toner is transferred to thetransfer member 13 and is overlapped onto the yellow toner image.

Moreover, the color-separation filter is exchanged in step n4 and thered color-separation filter 29c is installed for the greencolor-separation filter 29b and the light source lamp 21 is only turnedon in step n5 and the original document is scanned by the lightgenerated by the light source lamp 21 in step n6 so as to form anelectrostatic latent image. Onto the electrostatic latent image formedon the photosensitive member 1 is fed the cyanic toner from thedeveloping vessel 12c so as to be fixed and the toner image with thecyanic toner fixed is transferred to the transfer member 13, therebyforming a full color compound image with yellow, magenta and cyanictoners on the transfer member 13. The full color compound image withyellow, magenta and cyanic toners formed as described above has nooccurrence of a color irregularity since the quantity of the spectrum ofthe yellow wavelength band is increased by lighting the light sourcelamps 21 and 22 when the yellow toner image is formed, so that a goodimage can be obtained.

When the scanning operations of the original document is completed withthree steps having the blue, green and red color-separation filtersinstalled respectively, the color-separation filter is further exchangedin step n4. In case the blue color-separation filter 29a is one moreinstalled after the change of the filter in step n7, the scanningoperation of the original document for forming the full color image isfinished.

In this embodiment, though two light source lamps are provided, anynumber of light source lamps may be provided and the wavelength band inthe spectral distribution of the light generated by the light sourcelamp or lamps is determined in accordance with the quantity of thespectrum in the spectral distribution of the light of the light sourcelamp and with the spectral sensitivity of the photosensitive member. Inaddition, "means for turning on any one or more light source lamps"defined in the present invention corresponds to steps n1, n2 and n5.

As described above, according to the present invention, since any one ormore light source lamp or lamps of a plurality of the light source lampshaving different efficiencies respectively can be turned on inaccordance with the luminous energy of the spectrums of the respectivethree primary colors of blue, yellow and red in the light generated bythe light source lamps and/or the spectral sensitivity of thephotosensitive member so as to project an appropriate quantity of lightonto the original document, therefore, the difference among the luminousenergy of the blue, green and red spectrums in the light generated bythe light source lamp and the difference among the spectralsensitivities of the photosensitive member for the respective spectrumsof blue, green and red wavelength bands are compensated and theirregularity of the densities of the chromaticities of the image for therespective spectrums can be corrected so as to obtain a good imagewithout a color irregularity. Moreover, though the life time of a lightsource lamp with high efficiency is short, since the lamp may be lightedmerely for a short time when the quantity of the light is required to beincreased, the times of exchanging the lamps can be reduced.

What is claimed is:
 1. A light source device for use in a color copyingmachine in which a color image is formed in such a manner that a lightbundle is generated by said light source device to be projected onto anoriginal document and that the reflection light reflected by saidoriginal document is color-separated so as to be applied onto aphotosensitive member, said light source device comprising;a pluralityof light source lamps having different efficiency respectively and meansfor lighting any number of light source lamp or lamp among saidplurality of light source lamps depending on the luminous energy ofrespective spectrums of three primary colors of blue, green and red, inthe light generated by said light source lamps and/or on the spectralsensitivity of the photosensitive member for said respective spectrums.